1. Field of the Invention
This invention relates to a driver photographing apparatus for detecting driver's actions such as dozing, looking aside and the like.
2. Description of the Prior Art
FIG. 1 is a block diagram of an eye position detector using a prior art driver photographing apparatus shown in, for example, Japanese Published Unexamined Patent Application No. 158303 of 1985. In FIG. 1, reference numeral 1 designates a driver; numeral 2 designates a driver's seat; numeral 3 designates an instrument panel; numerals 10a, 10b designate CCD cameras; numeral 20 designates an infrared ray LED; numeral 21 designates an LED driving circuit supplying electric current to the infrared ray LED 20; and numeral 100 designates a driver's action detecting circuit.
Next, the operation of the prior art will be described.
The infrared ray LED 20 irradiates the driver 1 in the driver's seat 2. The images of the driver 1 are input to the CCD cameras 10a, 10b placed at the positions where the cameras 10a, 10b can photograph a prescribed region including the face of the driver 1. The input images to the CCD cameras 10a, 10b are further input to the driver's action detecting circuit 100 from the cameras 10a, 10b as image signals, then the data of eye positions, the directions of the face and the like are processed by means of image processing techniques. FIG. 2 is a sample of an infrared image obtained in such a way. In FIG. 2, reference numeral 4 designates an iris; numeral 5 designates a sclera; numeral 6 designates a pupil; and numeral 7 designates a face surface. In the image obtained in such a way, the sclera 5 is displayed a little darker in comparison with the face surface 7, and the iris 4 is displayed a little darker in comparison with the sclera 5, and further the pupil 6 is displayed still darker.
Because the prior art driver photographing apparatus is composed as described above, it has a problem that complicated image processing techniques are necessary to detect the positions of pupils 6. That is to say, the apparatus searches the pupils 6, for example, as follows: executing filtering operations, detecting edges, and pattern recognizing by executing the Hough transformation processing and the like for obtaining circles corresponding to the pupils 6 from the detected edge shapes. Moreover, the prior art apparatus has another problem that if the edges are not detected finely because of noises and the like at the time of the edge detection, the circles are not obtained and the image processings become very complicated, and time-consuming.
On the other hand, as shown in the article titled "THE EXTRACTION OF PUPILS AND A TRIAL PRODUCTION OF A SIGHT LINE DETECTING APPARATUS WHICH PERMITS THE MOVEMENTS OF HEAD PARTS" (DENSHI JOHO TUSHIN GAKKAI RONBUNSHI (TILE PAPERS JOURNAL OF THE ELECTRIC AND INFORMATION COMMUNICATION SOCIETY OF JAPAN), D-II, Vol. J76-D-II, No. 3), if a face is irradiated by a coaxially irradiating apparatus, images reflected on retinas can be clearly photographed, then positions of the pupil can be detected by very simple image processings such as, for example, transformation to a binary image from a grey image. (The "coaxially irradiating illuminating" means illuminating in a configuration where the optical axis of a camera and the irradiating direction of the illuminating light coincide with each other). It is accordingly thinkable to use this apparatus as a driver photographing apparatus, but the actual realization of it brings about a problem that the images reflected on retinas can not be obtained because there is disturbance light (or sunlight) whose light intensity is not less than 100 times through 1,000 times that of the illuminating light for photographing under the condition of being installed in cars. FIG. 3(a) and FIG. 3(b) are explanatory drawings for explaining influence caused by the aforementioned disturbance light. The waveshapes shown in FIG. 3(b) show the brightness distributions along the line A--A of an obtained face image (FIG. 3(a)). The curved line A of FIG. 3(b) designates the brightness distribution of a daytime image in fine weather which is photographed in the coaxially irradiating method; the curved line B designates the brightness distribution of another daytime image in rainy weather which is photographed in the same coaxially irradiating method; the curved line C designates the brightness distribution of a nighttime image which is photographed in the same coaxially irradiating method; and the curved line D designates the brightness distribution of another nighttime image which is photographed in an uncoaxially irradiating method (i.e. prior art construction). It can be found that the brightness of the parts of the images, other than the pupils 6, photographed in the coaxially irradiating method becomes higher in accordance with disturbance light's enlargement (the curved line C: in the nighttime .fwdarw. the curved line B: in the daytime in rainy weather .fwdarw.the curved line A: in the daytime in fine weather), and that the identification of the pupils 6 becomes correspondingly more difficult.